Weldable high strength magnesium base alloy



United States Patent Office 3,146,096 Patented Aug. 25, 1964 3,146,096WELDABLE HIGH STRENGTH MAGNESIUM BASE ALLOY George S. Foerster, Midland,Mich., assignor to The Dow Chemical Company, Midland, Mich, acorporation of Delaware No Drawing. Filed Nov. 23, 1962, Ser. No.239,829 4 Claims. (Cl. 75-168) These alloys combine moderate strength,good Workability in the wrought form, and are usable both for sheet andextrusions. Certain of these alloys have good weldability but in manyapplications must be stress relieved after welding to avoid stresscorrosion cracking. Other alloys such as, for example,

ZelOA (l.3Zn+0.2mischmetal) and AZlOA (1.25Al+0.4Zn) have been employedas substitutes where weldability without stress relief was required, butonly at a sacrifice of other desirable properties such as, for example,tensile and compressive yield strength.

The principal object of the present invention therefore, is to provide amagnesium base alloy having in community the properties of weldabilitywithout the need.

for stress relief, good workability, and desirable strength.

Known art teaches in general that if the concentration of thenon-magnesium constituents in a magnesium base alloy system of themagnesium-aluminum-zinc type containing manganese is increased,properties such as, for example, tensile and compressive strengths are,within limits, correspondingly increased. It has now been surprisinglyand unexpectedly discovered, however, that by reducing the aluminum andzinc concentrations of the alloys of magnesium base-aluminum-zinc-typecontaining manganese, below those conventionally employed and by addingsmall amounts of calcium thereto, alloys are obtained possessing theabove and other advantages in a combination heretofore not available inany one of the known magnesium base alloys within the aforementionedalloy system.

The present invention, then, resides in a magnesium base alloyconsisting by weight essentially of from about 0.1 to about 1.75 percentaluminum, from about 0.05 to about 0.6 percent zinc, from about 0.2 toabout 1.0 manganese, and from about 0.05 to about 0.6 percent calcium,the balance being magnesium, wherein the maximum concentration ofcalcium to be employed is in an inverse relationship with theconcentration of zinc used according to the formula:

Wt. percent Ca=1.42 (zinc percentage) Although the aluminumconcentration in the alloy need not be maintained in any relativeproportion with any of the other alloy constituents, if high extrusionspeeds are desired, suchas, for example, 50 to 100 f.p.m., generally thealuminum content must be limited in an inverse relationship withcalcium; that is, if either the aluminum or calcium concentration withinthe above respective ranges is high, the other of the two must be in arelatively low concentration. For example, it was found desirable tolimit the aluminum content to about 0.5 percent in order to obtain highextrusion rates when calcium was at a concentration of about 0.3percent. To obtain optimum extrudability, that is, high strength at highextrusion speeds, in the alloy of this invention it was found that thealuminum content should be 0.2 to 0.5 percent, the zinc content about0.2 to 0.5 percent, the calcium content from 0.2 to 0.4 percent, and themanganese content about 0.5 percent, the balance being magnesium.

The amount of aluminum relative to calcium in the alloy under thisinvention, however, has little effect on hot rollability and can be ashigh as about 1.75 percent, whereas the amount of zinc relative tocalcium must be maintained according to the aforementioned equation.However, good rollability can be obtained where the alloy containsrelatively high amounts of calcium if the zinc content does not exceedabout 0.3 weight percent, but at higher zinc concentrations, calciummust be limited by the said aforementioned equation to avoid crackingduring hot rolling.

Good creep resistance in the alloy of the invention was found to beobtainable, along with good workability, in the combination wherein theconcentration of the constituents in weight percent are about 0.4 foraluminum, about 0.3 for zinc, about 0.5 for manganese, and about 0.3 forcalcium.

On the other hand, the alloy of this invention exhibits good workabilityand ductility when the alloy composition consists essentially of about1.2 percent aluminum, about 0.3 percent zinc, about 0.5 percentmanganese, and about 0.2 percent calcium, the balance being magnesium.

Manganese is added to the alloy of the present invention to enhancestrength. The so added manganese also enhances corrosion resistance.

The present invention provides an alloy of flexible utility useful inapplications requiring an alloy of moderate to high strength plusweldability without the need of stress-relief, possessing goodworkability such as, for example, in extruding and rolling, and inaddition, being dilute in alloying constituent concentrations, itthereby offers economy along with utility.

The following examples serve to illustrate further the presentinvention:

A number of magnesium base alloys in accordance with the presentinvention and others as blanks for comparison were prepared usingconventional foundry alloying and melting techniques as practiced in themagnesium art and tested in various ways as shown hereinafter. Some ofthe so-prepared alloys were cast into 3 inch diameter billets, andothers into 2 by 4 by 8 inch rolling slabs. The billets were extrudedinto a 1A by inch strip at varying speeds from a 3 inch container atabout 700 F. Samples of the extrusions were tested both asextruded andafter having been aged for 24 hours at 350 F.

The slabs were hot rolled to about a 0.1 inch thickness at about 850 F.in a multitude of passes (with reheating as necessary to avoidcracking). The so-rolled sheet was then annealed for one hour at 900 F.,quenched in water, and cold rolled close to the cracking limit. Thesheet was then heat treated one hour at 300 F. and 700 F. Further, someof the same and other specimens were hot rolled and heat treated onehour at 950 F., quenched in Water, and aged 24 hours at 350 F.

Samples of all of the above preparations were tested 4 propertiesobtained when the hot holled sheet was subsequently solution heattreated, quenched, and aged as indicated showing improved ductility andtensile strength.

TABLE IV Creep Extension 1 Extension (in percent) subsequent to loadingwas measured at periodic intervals of time. The values of creepextension in Table IV were determined after a time of 100 ExamplePercent Percent Percent Percent Percent A Zn Ca Mn Creep hours.

1 In 100 hours at 300 F., stress at 5 kilo-pounds per square inch.

TABLE I Die x strip extrusions at 700 F. from a 3 billet 20 rpm.7100t.p.m. Percent Percent Percent Percent Percent Percent Example Al ZnCa Mn E IYS CYS TS Percent CYS TS TYS (Blank). 0. 5 4v 0 0.39 0. 6Cracked at f.p.m. (Blank) 0. 5 2.0 0.40 0. 0 Cracked at 10 f.p.m (1) 0.5 0. 5 0.33 0. 6 14 25 19 38 12 27 20 39 (2) n 0. 3 0. 5 0. 34 0. 6 1426 20 39 10 19 15 35 (3) 0. 3 0. 2 0.29 0.0 12 27 21 40 14 25 19 38 (4)0. 2 0. 4 0.20 0.0 13 27 18 39 13 78 19 40 1 Aged 24 hours at 350 F.

In Table I where Example Number 1 is compared with the examplestherefollowing, it is clearly shown that good extrudability is, ingeneral, obtained in the alloy of the present invention when therelative amounts of either zinc or aluminum, within their respectiveranges, are inversely related. That is, Example Number 1 shows thatexcessive zinc causes cracking at low extrusion speeds, whereas, whenthe concentration of zinc is within its specified range and in a properamount with respect to aluminum, the extrusion process can be carriedout at a relatively rapid Table IV illustrates the good creep resistanceof the alloy of the present invention, particularly when calcium withrespect to aluminum is low.

I claim:

1. A weldable high strength magnesium base alloy consisting by weightessentially of from about 0.1 to about 1.75 percent aluminum, from about0.05 to about 0.6 percent zinc, from about 0.2 to 1.0 manganese, andcalcium in an amount of from about 0.05 to about 0.6 percent but notgreater than 1.4 minus 2 times the percentage of zinc concentration, thebalance being magrate without cracking of the extrude. nesium.

TABLE II 1 300 F.1 hour 700 F.1 hour Percent Percent Percent PercentExample Al Zn Ca Mn Pcrltcnt TYS CYS 'IS Percent TYS CYS TS (Blank) 0. 54.0 0.39 0.0 (Blank) 0. 5 2v 0 0. 40 0. 6 Cracked during hot rolling(Blank) O. 5 1. 0 0. 31 0. 6 (5) 0. 3 0. 2 0.29 0. G 2 38 34 44 18 22 1935 l. 0 0. 6 0. 15 0. 6 4 37 34 44 22 23 18 35 0. 5 0. 2 0. 32 0. (i 241 30 47 13 24 18 36 0. 5 0. 5 0. 33 0. 6 4 41 36 48 12 25 19 3G 0. 5 0.2 0. 56 0. 6 2 43 40 20 24 20 37 1 Hot rolled at 850 F., annealed 1 hourat 900 F., quenched, cold rolled, then heat treated as indicated.

TABLE I11 Per- Per- Per- Per- Per- Example ecnt cent cent cent cent TYSCYS TS Al Zn Ca Mn E 1 Hot rolled at 850 F., solution heat treated 1hour at 950 F., quenched, aged for 24 hours at 350 F.

Table III also representatively shows the excellent 2. An extrudable andweldable high strength magnesium base alloy consisting by weightessentially of from about 0.2 to about 0.5 percent aluminum, from about0.2 to about 0.5 percent zinc, about 0.5 percent manganese, and calciumin an amount of from about 0.2 to about 0.4 percent, the balance beingmagnesium.

3. A creep resistant and weldable magnesium base alloy consisting byweight essentially of about 0.4 percent aluminum, about 0.3 percentzinc, about 0.5 percent manganese, and about 0.3 percent calcium, thebalance being magnesium.

4. A workable and weldable magnesium base alloy consisting by weightessentially of about 1.2 percent aluminum, about 0.3 percent zinc, about0.5 percent manganese, and about 0.2 percent calcium, the balance beingmagnesium.

References Cited in the file of this patent UNITED STATES PATENTS2,185,452 Wood Jan. 2, 1940

1. A WELDABLE HIGH STRENGTH MAGNESIUM BASE ALLOY CONSISTING BY WEIGHTESSENTIALLY OF FROM ABOUT 0.1 TO ABOUT 1.75 PERCENT ALUMINUM, FROM ABOUT0.05 TO ABOUT 0.6 PERCENT ZINC, FROM ABOUT 0.2 TO 1.0 MANGANESE, ANDCALCIUM IN AN AMOUNT OF FROM ABOUT 0.05 TO ABOUT 0.6 PERCENT BUT NOTGREATER THAN 1.4 MINUS 2 TIMES THE PERCENTAGE OF ZINC CONCENTRATION, THEBALANCE BEING MAGNESIUM.